Snap acting device



Filed June 26. 1950 2 Sheets-Sheet ,1

INVENTOR.

ATTORNEY.

Jan. 31, 1933. J. A. SPENCER SNAP ACTING DEVICE Filed June 25, 1930 2 Sheets-Sheet 2 Patented Jan. 31, 1933 UNITED STATES PATENT OFFICE JOHN A.- SPENCER, OF NEWTON, MASSACHUSETTS, ASSIGNOB TO m SPENCER Y THEBMOSTAT COMPANY, OF CAMBRIDGE, MASSACHUSETTS, A. COBPOBA'I'ION OF IASSACHUSETTS SNAP ACTING DEVICE Application ma June as, 1930. Serial in. mm.

This invention relates to snap-acting devices, and, with regard to certain more specific 'features to snap-acting devices, including snap-acting temperature responsive devices particularly adapted to operate valves,

switches, and the like, in response to ambient temperature variations of predetermlned range.

Among the several objects of the invention may be noted the provision of snap-acting, or overcentering devices, particularly thermostats, of the class described, which respond to suitable actuation with an improved snap or sudden action; whlch have a greatly increased range of action or. extent of throw; and which are sufiiciently resilient'or flexible in themselves to provide for the absorption of relatively slight movements, such as creeping, without causing undesirable movement of the device as a whole. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly "comprises .the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplifiedjin the structure-hereinafter described, and the scope of the application of which will be indicated in-the following claims.

In the accompanying drawings, in which ,is illustrated one of various possible embodiments of the invention, I

I Fig.4isa

Fig. 1 is a plan view of a snap-acting disc embodying the present invention;

Fig. 2 is a section taken along line 2-2 of Fi 5' i A Fig. 8 is an enlar ed diagrammatic showing of the stri pf ig. 5;

Fig. 9 is a iagrammatic elevation of the strip of Fig. 8; and,

.perature variations.

Fig. 10 is a diagrammatic section, similar to Fig. 2, showing certain characteristics of the disc embodiment of the invention.

Similar reference characters indicate corresponding parts throughout the several views of the drawings. y

In my prior Patent No. 1,448,240, granted March 13,1923, I have shown a snap-acting unit which is thermostatic or responsive to temperature changes,.comprising a disc of bimetal, or composite thermostatic material,

rovided with a non-developable portion. 11 response to the forces set up in the bi metal by temperature change, this non-developable portion undergoes a reversal of curvature, or change of flexure, with a sna This-device may also be snapped, by suita le application of external forces, without regard to-temperature changes. This prior patented device has proved quite satisfactory 1n practical usage. However, in In prior device, the extent of movement or throw of the device is somewhat small, and it can be increased onl by so greatly increasing the overall size 0 the device as to lead to an impracticable article.

The throw of a snap-acting device, such as a thermostat of this character is determined by the distance between its positions of staever, this depth. cannot be increased indefi nitely, as a point is soon reached where the normal resistance to reversal of curvature is in excess of thereversal force obtained thermally in the bimetal, whereupon the device will not change form in response to tem- The invention will be described principally by reference to its thermostatic embodiment, that is, where it performs in response to temperature changes. However, it will be understood that, even as a thermostat, the invention is fundamentally a snap-acting device.

The reversal force, or thermal force, is

set up by the differing linear expansions of the constituent metals of the bimetal. It is proportional to the area of bimetal in the given device. Thus, if the area ofbimetal in a given device may be increased, the thermal forces obtainable will be proportionally instatic material, such as bimetal, within a given overall size of device, and thus attains the desired result above set forth. Briefl the present invention rovides the increase area through corrugation of the bimetal.

Incident to this corrugation procedure, other advantageous results accrue, as will be pointed out hereinafter.

The invention is illustrated in this a plication in two of its embodiments, name y, a disc (Figs. 1, 2, 3, and 10) and a strip (Figs. 5, 6, 7, 8, and 9).

The disc embodiment of the invention comprises a sheet 10 of composite thermostatic material which is initially formed as a truncated cone, that is, the central portion of the disc is displaced or in a different plane than the peripher of the disc. The corrugations are rovide in radial arrangement as indicate by numeral 11, corresponding roughly to the elements of the basic truncated cone. Numeral 12 indicates the central hole of the disc, from and about which the corru ations 11 radiate. Desirably the disc 10 is ormed by corrugating a cylinder or the like and compressing one end of the cylinder inwardly, as this procedure rovides more com osite thermostatic materialin the inner region of mobility of the device, where it is most ad-- vanta eously employed. If a circular c linder used, it will be ap arent that the evelo ed inner periphery. o the device is even equa in length to t e developed outer periphe hvhen the predetermined temperature change of the device occurs, it snaps instantaneousl to a position of opposite curvature or stabi ity, indicated by dotted lines in Fig 3.

he disc embodiment thus shown is entirely self snapping, and requires no extraneous crtmfining or compression members to opera e. I

In 'Fi s. 5, 6, 7, 8 and 9 is illustrated the strip em odiment of the resent invention. A strip 25 of com osite t ermostatic material is provided wit crosaise corrugations,

as shown. The strip 25 is secured at its ends, 1n such manner as to be somewhat arched or bowed, to a support 26. The strip 25-carries,.

for example, a contact member 30, which cooperates with a relativel stationary contact 29 to control an electrical circuit (Fig. 6). It will be understood that this is but one of the manners in which the strip form of the present invention may be utilized.

Upon predetermined change of temperature, as in the case of the disc embodiment, the strip reverses the direction of its arch or curvature and snaps to the dotted line position (Fig. 5).

There are certain criteria which must apparently be fulfilled before either the disc or strip embodiments of the invention will snap back and forth in response to tem erature changes in opposite directions. or example, in Fi' 8 is shown an enlarged view of the strip em odiment. A series of imaginary lines or norms 31, located on each of the corru ations, determines an imaginary or norm sur ace 32, which may be considered to represent the strip with all of its corrugations flattened out. When the strip is in a position of stability, as in Fi 8, this ima inary surface is arched upward y. Ordinari y, the surface 32 ma be considered as lying'in the central axis 0 the corrugations, but its location varies as the shape of the corrugations and other factors vary.

In order for the strip to snap back and forth, as desired, the surface 32 must be ca pable of undergoing a decrease in area to a minimum, when it is fiat, and when it represents a central condition ,of instability of the strip (Fig. 9). After passing through this position of minimum area, the surface 32 must again increase in area, but in an opposite direction, corresponding to the opposite or second position of stability of the strip. Throughout all of this change of area and position of the surface 32, the disposition of the corrugations on either side thereof should not change substantially.

If the conditions above indicated are met, the strip will, upon rise of temperature to a predetermined value, sna from one position of stability through its position of in- ,stability to its second position of stability,

in the disc form, instead of being in the form of a simple arch, resembles an uncorrugated, truncated cone. Its devolution, to a flat, central position of instability, represents a decrease in area to a minimum value, and its subse uent increase in area carries it to the secon position of stability of the disc. As

in the strip form, the disposition of the corrugations on both sides of the surface 32 should remain substantially unchanged from position of stability throu h position of instability to alternate position of stability.

Thus constituted, the disc form of the invention is likewise capable, upon increase of temperature, of snapping from one position first position of stability, an automatically ous forces. 7

It will be seen that, when the thermostat is so constructed as to com ly with the above conditions, it is so forme (either strip or disc) that it can be flattened without temperature change. only by compressing the corrugations to such a position that the device is in an unstable position.

The term composite thermostatic material as used herein is accordingly defined as a sheet of two or more layers of metals having difl'erent coeflicients of thermal expansion. When two layers are used, the material is commonly called-bimetallic. It is to be understood that the several layers need not be in discrete steps, a material having a varying composition throughout its cross section (such as disclosed in the patent issued to Vannevar Bush, No. 1,870,235, dated August 9,1932), being likewise contemplated by the term composite thermostatic material. As the disc or strip is formed, for use where the normal position is cold, the component. of the thermostatic material having the higher coefiicient of thermal expansion is, in the'cold position of the thermostat, located upon the concave side of the strip or disc.

If the invention is to be employed as a simple mechanical snap-acting or overcentering device, or spring, it will readily be seen that the use of composite thermostatic metal is unnecessary, although possible. In such 1nstances,a sheet of single resilient metal may be used with success. The action of the deand without the applicationof any extranevice as an overcentering element needs no.

further description, as it varies from the thermostatic element only in that applied ex-' 1 ternal forces replace the self-engendered thermostatic forces in effecting the change of shape desired. 7

' In view of the-above, it will be seen that the several objects. of the inventionare achieved and other advantageous results attained. i

As many changes could be made in carrying out the above constructions without dearting from the scope of the invention, it is untended that all matt r'contained. in the above description or sho mg drawingsflsha'll-b'e interpreted as illustrative and not in a limiting sense.

I claim:

-- '1. A thermostat'comprising a sheet of com- .0 posits thermostatic material havin a large Ii in the accompany: I

lines 'on said corrugations, within the en velopes of said, corrugations, has two separate positions of relatively lar e area, establishing two positions of stabi ity of the device, and an intermediate position of mini-' mum area, establishing a position of instability of the device, the said corrugations bein 'so formed that they are disposed on both si es of said surface in substantiall the same manner in both positions of stability and in the intermediate position of instability, said device thereby automatically snapping, up-

on change of temperature in one directlon, from'one position of stability through the position of instability to the second position 'of stability, and automatically snapping, u on c'han e of temperature in the reverse direction, rom said second position of stability through the position of instability back to the said first position of stability. y I

2. A thermostat as set forth in claim 1 in which the thermostatic sheet is in the form of a strip, held at its ends between relatively rigid abutments, and in which the corruga tions are at an angle to the length of the strip. 1 I

3. A thermostat as set forth in claim 1 in which the thermostatic sheet is in the form of a-disc, and the corrugations are positioned radially on the disc. i

4. A-thermostatic unit comprising a sheet of composite thermostatic material formed of two layers of different coefficients of thermal expansion, and shaped in the form of .a truncated cone with an opening at its apex, the unit having its surfaces corrugated and being adapted to assume a position of opposite configuration under influence of temperature changes of predetermined ranges.

5. A snap-acting bimetallic thermostatic disc in the form of a truncated cone having a hole at its apex, the disc having itssurfaces' corrugated and being capable of automati cally assuming a position of opposite config- J1 uration under influence of temperature changes of predeterminedrange.

6. Athermostat comprising a disc of composite thermostatic material I having radial corrugations therein, the plane of the central portion of said disc being displaced from theplane of the eripheral portion thereof, whereby said isc is adapted at predetermined respective critical temperatures to assumepositions of; opposite configuration.

7. I thermostat comprisin a disc of composite thermostatic material aving the general shape of a cone and havin at east part of its surface corru ated, said two positions of sta le equilibrium and. an intermediate position of unstable equilibrium, said disk being adapted toassume said positions of stable equilibrium under influence of. temperature. changes of apredetermined range. 7

8. A snap-acting thermostat comprising disk having.

an annulus of composite thermostatic material, the annulus being so bent that its inner and outer developed peri heries are of substantially e ual lengths, sai annulus having the plane 0 its inner periphery displaced from the plane of its outer periphery.

Y 9. A snap-acting thermostat comprising an annulus of composite thermostatic material, said annulus being corrugated and havin the plane of its central portion displaced from the plane of its peripheral portion.

10. A thermostat comprising a frustum of a cone formed of composite thermostatic material, said frustum being so corrugated that its developed internal periphery is greater in length than the developed internal periphcry of a smooth-surface frustum of equivalent size.

11. A snap-acting device comprising a disc of resilient material having radial corru ations therein, the plane of the central portlon of said disc bein displaced from the plane of the periphera portion thereof, the said disc being suitably resilient, whereby upon suitable actuation thereof, it overcenters to assume a position of opposite configuration.

12. A snap-acting device comprising an annuluspf resilient material, the annulus bemg so bent that its inner and outer developed peripheries are of substantially equal lengths,

said annulus having the plane of its inner periphery displaced, from the plane of its outer periphery.

In testimony whereof, I have signed my name to this specification this 25th day of June, 1930. 1 J OHN A. SPENCER. 

